This invention relates, in general, to semiconductor devices, and more particularly, to a method for a flip chip device and method of manufacture.
As the need for smaller and more efficient semiconductor devices increases, the desirability of using power copper structure in those devices also increases. This is due to the fact that power copper devices dissipate heat more efficiently than other devices. Also, power copper devices have relatively thick copper structures which have a lower impedance than typical semiconductor aluminum interconnections.
Not only is there a demand for power copper devices, there is also an interest in power copper devices which can be packaged as flip chips. A flip chip is a semiconductor that has solder pads built on and, therefore, can be directly soldered onto another component instead of using wire bonding or similar technique. However, combining the two technologies, power copper and flip chip design, has proven difficult.
One proposed solution is to place solder directly onto the power copper structure. However, when this approach is used, the solder bumps collapse during assembly to the substrate. This is because copper is a wettable surface which causes the solder bump to collapse and spread out over the copper. To avoid solder bump collapse, adding a layer of polyimide has been proposed. However, the polyimide does not adhere well to metals and contains polyimide acids which work to cause copper dissolution in the power copper structure. Clearly a need exists for solutions to the aforementioned problems.